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If the mobile phone is leaving a
UMTS cell and it cannot find a new UMTS cell then the base station can hand
over an appropriately equipped mobile phone to a cell in another system.
These intersystem handovers are highly complex because two technically
disparate systems must be combined with each other. Basically, there are two
handover options from WCDMA to GSM:
In the case of blind
handover, the base station simply transmits the mobile phone with all
relevant parameters to the new cell. The mobile phone changes “blindly” to
the GSM cell, i.e. it has not yet received any information about the timing
there. It will first contact the transmitted BCCH channel, where it tries to
achieve the frequency and time synchronization within 800 ms. Next, it will
switch to the handed-over physical voice channel, where it will carry out the
same sequence as with the non-synchronized intercell handover.
For the second type of handover
from WCDMA to GSM, the compressed mode is used within the
WCDMA cell; in this mode, transmission and reception gaps occur during the
transmission between base station and mobile phone. During these gaps, the
mobile phone can measure and analyze the nearby GSM cells. For this purpose,
the base station, similar to the GSM system, provides a neighbour cell list,
and the mobile phone transfers the measurement results to the base station.
The actual handover in the compressed mode is basically analogous to blind
handover.
There is, of course, an
intersystem handover from GSM to WCDMA. A special neighbour cell list for
WCDMA cells was established in GSM to support this handover.
I have a small query related to IRAT HO.I just
need to know what we can do to control the number of IRAT HO from 3G to 2G in
some particular cells if they are at border and non border? I know that we
can change some RNC parameters to change the GSM threshold,but more
interested to know about Cell Level Parameters and the cells which are in the
middle of a city. Give me some thoughts and idea? I want to reduce the number
of IRAT HO from 3G to 2G at some of my downtown cells!!! - Arun Verma in
Yahoo Groups: UMTS
Answered by Kamal Vij in Yahoo
Groups: UMTS
As u might be well aware of , in
UMTS UE always tries to do Intra-freq. HO. And to trigger an Inter Freq and
Inter RAT there are several triggers /threshold criteria which must be
fulfiulled.
For example, theCPICH EcNo
coverage is very "BAD", CPICH RSCP coverage is "BAD", the
UE is using very "HIGH" transmission power and is close to
saturation, DL transmission power for that particular radio link is very
"HIGH" and so on...
The words "BAD" and
"HIGH " are defined by cell level thresholds. I cant write more
precisely because it goes beyond the privacy agreements with my customer.
Please try to look for the
Parameters which define Inter System THRESHOLDS .
For example , consider CPICH EcNo.
Genrally -8 is very good coverage,
-12 is ok, and -15 EcNO is just close to the coverage hole.
Att -13 u may start Inter RAT. If
u allow the mobiles to survive in 3G even if the coverage is -14 dB (almost
close to coverage hole), u can save a lot of Inter RAT handovers.
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